In recent years, magnetic recording/reproducing machines have been widely used. Accordingly, inferior adjustment of the magnetic recording medium running system often takes place with magnetic recording/reproducing machines.
When the axes of a magnetic recording/reproducing machine, which are placed on the running passage for the magnetic recording medium (such as a feed reel axis, a tension stabilizer guide axis, a revolving head cylinder axis, a pinch roller axis, a capstan axis, a running guide axis or a winding reel axis, etc.) cause a minute warp at the normal axis position, the magnetic recording medium suffers minute damage. This damage can increase the audio output variation, if the magnetic recording medium is allowed to run in such a magnetic recording/reproducing machine. Further, damage is formed in control tracking for controlling rotation of the video head (namely, the control tracking is damaged so that the servomechanism does not operate normally)which causes jitter and time base errors, etc. This minute damage in the magnetic recording medium generally causes audio output variation and inferior tracking control over the passage of time. As a result, creases like seaweed and formed on the edges and end parts in the width direction of the magnetic recording medium.
Hitherto, the audio output variation and/or the inferior tracking control was improved by reducing the friction coefficient of the magnetic recording medium, namely, by improving the surface lubricating property, as described in Japanese Patent Application (OPI) Nos. 154632/82, 119930/81, 124122/81 and 124126/81 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). In order to improve the surface lubricating property, a desired lubricant was uniformly blended and/or dispersed in a coating solution and applied to a polyester base. Alternatively, the lubricant was dissolved in a solvent and applied as an overcoating layer to the surface of the polyester base to which the coating solution had been applied and/or the back thereof.
As the lubricant, aliphatic acids and/or aliphatic acid esters having a melting point of 100.degree. C. or less, etc., were used. However, it was difficult to obtain magnetic recording media having sufficient characteristics, even though these additives were used. Furthermore, when these additives were used in a large amount in order to increase the lubricating effect, mechanical strength of the recording layer sometimes deteriorated.
Thus, as a result of analyzing in order to improve the audio output variation and/or the inferior tracking control of the magnetic recording medium, the present inventors have found that it could be attained by improving ununiform running tension in the width direction of the magnetic recording medium and by controlling the friction characteristics of the edges and cutting section of the magnetic recording medium. These facts indicate that the audio output variation and the inferior tracking control cannot be improved, even if the surface lubricating property of the magnetic recording medium is improved.
Namely, in studying the magnetic recording/reproducing machine in detail, it is understood that the surface and the cutting section of the magnetic layer in the magnetic recording medium pass in contact with various kinds of material. Further, it is very difficult to give a good lubricating property for all materials with respect to the surface of the magnetic layer using the same lubricant, though it is applied to the same surface of the magnetic layer. Namely, the magnetic face of the magnetic recording medium generally runs in contact with an audio head and a control head in the edge portions thereof and with a video head in the central part thereof. Further, the edge portions of the magnetic face runs in contact with various kinds of materials such as a stainless guide pole, a flange, ceramics, synthetic resins, aluminum alloys, resin processed goods, etc. Namely, in order to give a satisfactory lubricating property for such materials to the magnetic recording medium, it is possible to properly use a lubricant suitable for materials contacting with the surface of said magnetic layer. The present inventors have now found that the lubricating property suitable for contacting materials can be obtained by applying a carboxylic acid or a carboxylic acid derivative to both edge portions or one edge portion of the surface of the magnetic layer in the magnetic recording medium and applying, for example, aliphatic acids, aliphatic acid esters, silicone, phosphoric acid esters, etc., to the central part.